Tagawa M, Brown C L
Division of Applied Biosciences, Graduate School of Agriculture, Kyoto University, Kitashirakawa, Sakyo-ku, 606-8502, Kyoto, Japan.
Comp Biochem Physiol B Biochem Mol Biol. 2001 Jun;129(2-3):605-11. doi: 10.1016/s1096-4959(01)00352-9.
The patterns of entry of thyroid hormones into live tilapia oocytes were examined by incubating ovarian follicles in L-15 medium containing 125I-labeled thyroxine (T4) or 3,5,3'-triiodothyronine (T3). As judged from HPLC profiles, radioactivity in extracts of follicles immersed in T3 was identified to reside in T3, while most of the radioactivity in the extract of T4 immersed follicle was not associated with T4. Radioactivity of T3 immersed follicles reached a constant level after 18 h of incubation. Entry of T3 into the oocytes was non-saturable within the range of 0.5-5000 ng/ml of T3 in the incubation medium, suggesting the absence of specific mechanisms for T3 entry into the oocyte. Presence of female plasma at a level of 20% of incubation medium inhibited the T3 entry into the oocytes by approximately 80%. When follicles were back-transferred to medium without T3, only 15% of T3 in the oocyte disappeared within the following 24 h. From our results, we conclude that free T3 seems to enter oocytes freely across the membranes by diffusion, and that T3 in the oocytes may bind to some molecules in the oocyte. However, during egg formation in vivo, contribution of free T3 entry into the oocytes did not seem to be significant when considering the free T3 ratio in female plasma.
通过将卵巢卵泡在含有125I标记的甲状腺素（T4）或3,5,3'-三碘甲状腺原氨酸（T3）的L-15培养基中孵育，研究了甲状腺激素进入活罗非鱼卵母细胞的模式。从高效液相色谱图判断，浸泡在T3中的卵泡提取物中的放射性被鉴定为存在于T3中，而浸泡在T4中的卵泡提取物中的大部分放射性与T4无关。浸泡在T3中的卵泡在孵育18小时后放射性达到恒定水平。在孵育培养基中T3浓度为0.5-5000 ng/ml范围内，T3进入卵母细胞的过程是非饱和的，这表明不存在T3进入卵母细胞的特异性机制。当雌性血浆以孵育培养基20%的水平存在时，T3进入卵母细胞的过程受到约80%的抑制。当卵泡重新转移到不含T3的培养基中时，卵母细胞中只有15%的T3在接下来的24小时内消失。从我们的结果来看，我们得出结论，游离T3似乎通过扩散自由穿过膜进入卵母细胞，并且卵母细胞中的T3可能与卵母细胞中的某些分子结合。然而，在体内卵子形成过程中，考虑到雌性血浆中的游离T3比例，游离T3进入卵母细胞的贡献似乎并不显著。
